The castle is situated on a rocky island in Loch Moidart which is accessible at low tide across a sandy spit, hence "tioram", the Gaelic word for "dry".
It is one of the group of curtain-wall castles, together with neighbouring Mingarry in Ardnamurchan, with massive masonry of stone and lime construction, of plan shape reflecting the natural outline of the site, impressive wall defences, a tactically defended landward entrance, and substantial courtyard buildings. Its perspective is seaward and maritime, as with so much of the political and cultural history of the western seaboard of the Gaidhealtachd - its seagate, a notable characteristic of West Coast castles, more obvious from the seaward side - making the structure in its massing of historical and architectural elements one of the most remarkable emblems of Highland history.
The curtain walls of the castle, thought to date to the 13th century, form an irregular pentagon fitting the
rocky summit of Eilean Tioram.
The situation commands the junction of Loch Moidart with the mouth of the River Shiel.
Below the northwest wall is a beach allowing ships to be brought close in to transfer supplies or people.
The buildings within the curtain walls were added between the 14th and 17th centuries, beginning with the tower house built into the southeast wall and finishing with the decorative turrets of the seaward western tower.
The sequence of architectural changes before 1715 has been followed by more minor changes since that date. 18th century plans to convert the castle into a government fort fortunately were not implemented. A phase of neglect, during which the castle was robbed of some of its worked stone, such as lintels and fire surrounds, followed; then early conservation works in the 19th century, which unfortunately cleared out all the archaeologically interesting debris within the castle. In the 20th century the Ministry of Works carried out conservation work in the 1920s and 1950s, while the present owner has repaired a stonefall from the northwest curtain of 1999.
The result is that the castle is generally remarkably well-preserved, with all walls standing to nearly full height; though its wall surfaces have been altered significantly over the past 200 years this is not immediately apparent.
The Stell Report: Interpretation, Historic Scotland